Electrostatic discharge (ESD) is a natural phenomenon in daily life. In ESD, in a short time, heavy currents will be generated, causing fatal damage to ICs, and even causing malfunction in ICs' manufacturing and application. For example, when the ESD occurs on human body (short for HBM), the discharge usually occurs in a time of only hundreds of nanosecond and the current peak can reach several amperes. Other modes of ESD, such as the MM and the CDM, the discharge time is even shorter and thus the current is heavier. Such heavy current flows through the IC in a short time usually results in power consumption seriously exceeding the maximum endure value of the IC, and thus cause serious physical damage to the IC and lead to malfunction.
Two main aspects, including environment and circuitry, are considered to lighten the impact caused by the ESD. As for the environmental aspect, reducing the generation of electrostatic and timely elimination of the electrostatic could be used. For example, to use materials difficult to generate electrostatic, to increase the environment humidity, to ground the operating staff and the apparatus etc. While as for the circuitry aspect, the major consideration is to increase the ESD enduring ability of the IC itself. For instance, to add additional electrostatic protection apparatus or circuit to protect the inner circuit of the IC from being damaged by the ESD.
For the apparatus used for high voltage IC ESD protection, several important parameters shall be noticed. The first shall be the blocking voltage. High blocking voltage will keep the apparatus staying at a high-impedance state when the apparatus works in a normal high voltage, therefore the normal work of other circuits are not affected. The second shall be the trigger voltage. Proper trigger voltage shall be incorporated in order to protect the inner circuits. Thirdly, the sustaining voltage shall be higher than the working voltage, to prevent the effect of latching up. The fourthly consideration shall be the sufficient self-protection ability to protect itself from being affected by ESD. Conventional apparatus used for high voltage ESD protection, such as SCR, Diode, LDMOS etc., usually cannot meet the requirement of all the considerations mentioned above. For example, as the sustaining voltages of the SCR and the LDMOS are comparatively low, it is easy to cause the effect of latching up which will lead to malfunction of the circuit even the IC works in a normal state. As to the Diode, it would probably cost large device area in order to achieve sufficient self-protection ability thereof.